Field of the Invention
The present invention relates to a sheet punching device configured to punch a hole in a sheet, and an image forming apparatus including the sheet punching device in a main body of the apparatus.
Description of the Related Art
Conventionally, some image forming apparatus configured to form an image on a sheet include a sheet punching device configured to punch a hole in the sheet in a main body of the apparatus.
The sheet punching device includes a rotary type sheet punching device which punches a hole in a sheet by rotating a die and a punch at the same time (see Japanese Patent Application Laid-Open No. 2001-179690) and a press punch type sheet punching device which includes a punch and a die arranged opposite to each other while interposing a sheet therebetween and moves the punch in a direction perpendicular to the sheet to punch a hole in the sheet (see Japanese Patent Application Laid-Open No. 2001-26370).
However, the rotary type sheet punching device and the press punch type sheet punching device have the following features and problems.
That is, the rotary type sheet punching device punches a hole in the sheet by rotating the die and the punch at the same time, and hence it is possible to punch a hole in the sheet while keeping on conveying the sheet, thus providing a feature of high punching efficiency. However, the die and the punch are engaged with each other while being rotated, and hence a tip portion of the punch and an entrance portion of a die hole of the die need to be formed normally into involute curve shapes as in an engagement of gears. When the tip portion of the punch and the entrance portion of the die hole are formed into the involute curve shapes, a clearance is generated therebetween, and hence it is difficult to punch the hole with accuracy.
On the other hand, the press punch type sheet punching device punches a hole in the sheet by moving the punch in the direction perpendicular to the sheet, thus providing a feature that a hole of an accurate shape can be punched in the sheet. However, the press punch type sheet punching device cannot punch the hole without temporarily stopping the sheet which is being conveyed, thereby posing a problem of low punching efficiency.
Therefore, there has been a demand for a sheet punching device which takes advantage of the features of both types of sheet punching devices while solving the problems inherent therein.